1. Technical Field
The present invention relates generally to a method of manufacturing semiconductor devices and, specifically, to a method of forming films such as silicon oxide films used in the manufacture of such devices, the films having a tunable dielectric constant.
2. Description of the Related Art
Chemical vapor deposition (CVD) is a commonly used technique for forming thin films and has been widely used as a manufacturing technique in the semiconductor device industry. CVD methods using an organic or inorganic silicon compound gas and an oxidizing gas are well known as methods for forming thin films of silicon oxide. In such semiconductor devices, an insulating film is typically utilized for electrically isolating element wiring. The typical insulating film used in the past was a SiO.sub.2 film formed by the thermal oxidation of a silicon substrate or a SiO.sub.2 film formed by chemical vapor deposition under a reduced pressure or atmospheric pressure using gaseous materials such as silane and tetraethoxy silicate (TEOS). Particularly in the case of aluminum wirings, SiO.sub.2 films are preferred for insulation and are formed by CVD techniques using either TEOS or silane and O.sub.2 because such SiO.sub.2 films can be formed under temperatures as low as about 400.degree. C.
As transistors are scaled into the submicron regions in such semiconductor devices, the interconnect spacing between wiring is reduced so that electromagnetic coupling of adjacent metal lines is possible causing errors, noise and, in the extreme case, a non-functioning device. As the space between two adjacent metal lines is shortened in accordance with the miniaturization of the semiconductor circuitry, increased capacitance occurs between the metal lines tending to obstruct the higher operating speed of the semiconductor device, thereby inhibiting the performance improvement offered by the miniaturization of the device.
As a result of these shortcomings, it is often important to decrease the dielectric constant of the insulating film which is interposed between two adjacent lines in a semiconductor device. The SiO.sub.2 film formed by conventional plasma CVD methods typically has a dielectric constant in the range from about 4.0 to 5.0. The higher the dielectric constant of the oxide film, the further the electromagnetic field can penetrate into the dielectric media. By reducing the dielectric constant of the oxide, two interconnect lines can be placed closer in proximity, thus lowering the operating voltage of the transistor because the noise margin thereof can be reduced. It is desirable, therefore, in some instances to reduce the dielectric constant of such films from approximately 4.5 to about 3.0 or lower.
Contrarily, it is sometimes desirable to increase the dielectric constant of the oxide film being formed in semiconductor devices such as capacitors. The higher dielectric constant materials can be used to form regions of capacitance within the integrated circuit. The higher the dielectric constant of the material, the smaller the capacitance region required, resulting in a smaller capacitor, thereby equating to an area savings.
The dielectric constant of oxides can be lowered by the addition of carbon or fluorine into the oxide. While this general principle has been stated in the prior art, the previous attempts to provide a film having a lowered dielectric constant have exhibited various deficiencies. For example, in Japanese Patent Application No. 2-77127, fluorine is introduced into SiO.sub.2 by means of ion implantation. However, it is necessary to apply a heat treatment at a temperature of at least about 600.degree. C. within the SiO.sub.2 layer. Thus, the SiO.sub.2 layer formed by this method cannot be used for isolation of aluminum wirings within semiconductor devices.
In U.S. Pat. No. 5,429,995, issued Jul. 4, 1995 and assigned to Kabushiki Kaisha Toshiba, a method is shown for manufacturing a semiconductor device with a film which exhibits a low dielectric constant which uses FSi (OC.sub.2 H.sub.5).sub.3 as the silicon source gas. A particular object of the invention was to provide an insulating film having low hygroscopicity. It would be desirable, however, to use as the organic silicon source gas a conventional TEOS to allow conformal coverage and to provide a process which can be run on any of the conventional PECVD type deposition systems.
Additionally, in certain of the prior art techniques, it has been difficult to control accurately the fluorine concentration in the SiO.sub.2 film.
Accordingly, it is an object of the present invention to provide a method for forming a SiO.sub.2 film which has a tunable dielectric constant and which is formed by conventional plasma CVD methods using TEOS as the silicon source gas or which is formed by either HDP (high density plasma) or atmospheric pressure chemical vapor deposition (APCVD) methods using a silane as the source gas.
Another object of the invention is to provide a method for manufacturing a semiconductor device in which a silicon oxide film containing fluorine and carbon is produced, the film acting as an insulating film for electrically isolating conductive layers included in the semiconductor device, the film being formed by plasma CVD technique using an organic silicon gas as a starting material.
Another object of the invention is to provide basic nitrogen incorporation to act as a moisture and OH barrier for the activating film.
Another object of the invention is to provide a lower dielectric constant film which is stable with higher concentrations of fluorine incorporated into the film.
Another object of the invention is to provide a method of manufacturing semiconductor devices in which the conductive layers on the silicon oxide films so produced have improved reliability.